1. Field of the Invention
The invention relates to the field of binder compositions utilized in the manufacture of fiber products, typically from glass fibers. Specifically, the invention relates to a poly alcohol-based aqueous binder composition and fiber products incorporating such a binder composition.
2. Background Information
Manufacture of glass fiber thermal insulation typically utilizes a continuous process in which raw batch materials are fed into a melting furnace to produce molten glass. The molten glass is then ejected from the furnace through a number of trays or bushings having small openings to form glass filaments. The initial glass filaments are then typically pulled and attenuated to produce the final fiber dimensions and cooled to form the glass fibers. The cooled fibers are then collected on a conveyor belt to form a mat.
The fibers are typically bonded together to form an integral batt or layer structure by applying a binder composition to the fibers as they are being collected on the conveyor belt. The collection of binder-coated fibers is then cured, typically in a curing oven, to evaporate remaining solvent and set the binder composition. The fibers in the resulting fiber product thus remain partially coated with a thin layer of the binder material and may exhibit greater accumulation or agglomeration at junctions formed where adjacent fibers are in contact or the spacing between them is very small. As a result of the improved strength and resiliency, the resulting fiber products exhibit higher recovery and stiffness than fiber products that do not incorporate a binder.
Fiberglass insulation products prepared in this manner can be provided in various forms including batt, board (a heated and compressed batt) and molding media (an alternative form of heated and compressed batt) for use in different applications. Most fiberglass batt insulation will have a density of less than 1 lb/ft3 (16 kg/m3) with about 4-5 wt % being binder. Fiberglass board typically has a density of between 1 and 10 lbs/ft3 (16 and 160 kg/m3) with about 7-12 wt % binder while fiberglass molding media will more typically have a density between 10 and 20 lbs/ft3 (160 and 320 kg/m3) with at least about 12 wt % binder. The glass fibers incorporated in these products typically have diameters from about 2 to about 9 microns and may range in length from about 0.25 inch (0.64 cm) to the extremely long fibers used in forming “continuous” filament products.
As the batt of binder-coated fibers emerges from the forming chamber, it will tend to expand as a result of the resiliency of the glass fibers. The expanded batt is then typically conveyed to and through a curing oven in which heated air is passed through the insulation product to cure the binder. In addition to curing the binder, within the curing oven the insulation product may be compressed with flights or rollers to produce the desired dimensions and surface finish on the resulting blanket, batt or board product. In the case of molding media, after partially curing the binder, the fiber product is fed into a molding press that will be used to produce the final product shape and to complete the curing process. Typically, for fiber products incorporating phenolic binders the curing ovens were operated at a temperature from about 200° C. to about 325° C. and preferably from about 250° C. to about 300° C. with curing processes taking between about 0.5 minute and 3 minutes.
Generally, the goal is to identify a binder system that is relatively inexpensive, is water soluble (or at least water dispersible), and can be easily applied and readily cured. The binder composition should also be sufficiently stable to permit mixing and application at temperatures ordinarily encountered in fiber product manufacturing plants. Further, the cured binder product should result in a strong bond with sufficient elasticity and thickness recovery to permit reasonable deformation and recovery of the resulting fiber product. Thickness recovery is especially important in insulation applications for both conserving storage space and providing the maximum insulating value after installation.
Phenol-formaldehyde binders, which are characterized by relatively low viscosity when uncured and the formation of a rigid thermoset polymeric matrix with the fibers when cured. A low uncured viscosity simplifies binder application and allows the binder-coated batt to expand more easily when the forming chamber compression is removed. Similarly, the rigid matrix formed by curing the binder allows a finished fiber product to be compressed for packaging and shipping and then recover to substantially its original dimension when unpacked for installation.
Phenol/formaldehyde binders utilized in the some prior art applications have been highly alkaline resole (also referred to as resol or A-stage) type that are relatively inexpensive and are water soluble. These binders are typically applied to the fibers as an aqueous solution shortly after the fibers are formed and then cured at elevated temperatures. The curing conditions are selected to evaporate any remaining solvent and cure the binder to a thermoset state. The fibers in the resulting product tend to be partially coated with a thin layer of the thermoset resin with accumulations of the binder composition being found at the junctions formed at points where adjacent fibers cross.
Various techniques have been used to reduce formaldehyde emission from phenol/formaldehyde resins including various formaldehyde scavengers added to the resin during or after its preparation. Urea is a commonly used formaldehyde scavenger that is effective both during and subsequent to the manufacture of the fiber product. Urea is typically added directly to the phenol/formaldehyde resin, to produce a urea-extended phenol/formaldehyde resole resin (also referred to as “premix” or “pre-react). Further, urea, being less expensive than the alkaline phenol/formaldehyde resoles commonly used as binders, can provide substantial cost savings for fiber product manufacturers.
Low molecular weight, low viscosity binders which allow maximum vertical expansion of the batt as it exits the forming stage generally form a non-rigid plastic matrix when cured and reduce the vertical height recovery properties of the final product. Conversely, higher viscosity binders tend to cure to form a rigid matrix that interferes with the vertical expansion of the coated, but uncured, fiber batt.
These problems were addressed with a variety of non-phenol/formaldehyde binders exhibiting low uncured viscosity and structural rigidity when cured. One such binder composition was disclosed in U.S. Pat. No. 5,318,990, which is herein incorporated, in its entirety, by reference, and utilized a polycarboxy polymer, a monomeric trihydric alcohol and a catalyst comprising an alkali metal salt of a phosphorous containing organic acid. Other binder compositions have also been developed to provide reduced emissions during the coating and curing processes utilizing compounds such as polyacrylic acid as disclosed in U.S. Pat. Nos. 5,670,585 and 5,538,761, which are herein incorporated, in their entirety, by reference.
Another binder composition is disclosed in U.S. Pat. No. 5,661,213, which teaches an aqueous composition comprising a polyacid, a polyol and a phosphorous-containing accelerator, wherein the ratio of the number of equivalents of the polyacid to the number of equivalents of the polyol is from about 100:1 to about 1:3.
As disclosed in U.S. Pat. No. 6,399,694, another alternative to the phenol/formaldehyde binders utilizes polyacrylic glycol (PAG) as a binder. Although more expensive, PAG binders are relatively odorless, more uniformly coat each fiber and have a generally white color. These characteristics, coupled with the recognition that coloring agents adhere readily, make PAG binders preferable for applications in which the fiber product will be visible after installation. Indeed, fiber board products utilizing PAG binders can be provided with decorative surfaces suitable for display.
The use of polyacrylic acid based binders, however, has resulted in corrosion problems in manufacturing equipment. Thus, there continues to exist a need for a method of inhibiting and reducing the corrosion associated with these prior art binders.